This invention relates to a braking pressure control unit for a pressure-medium-operable vehicular brake system. The unit is actuatable in a load-responsive manner by way of a spring device which may be temporarily blocked and which may be hinged to a vehicle part carrying out relative movements with respect to the braking pressure control unit. The unit includes at least one valve with a control piston displaceable in a pressure-dependent manner in the closing direction against the force of the spring device hinged to a swivelling transmission lever. The unit includes an actuating device by means of which the force of the spring device by means of which the force of the spring device is variable and which comprises a first actuating element connectible with the vehicle part, a second actuating element associated with the transmission lever, and a spring arranged between the elements.
In European Pat. (EP) No. 00 29 398 B1 a braking pressure control unit of the type referred to above is disclosed which essentially comprises a first actuating element connectible with an unsprung part of the vehicle, and a second actuating element which is connected by way of the spring device designed as a tension spring with the transmission lever supported at the housing. An auxiliary spring is arranged between the first and second actuating elements. When assembling the braking pressure control unit, with the spring device being blocked, the housing is fastened at a spring-mounted part and the first actuating element is fastened at an unsprung part of the vehicle. During assembly a removable stop ring is arranged at the first actuating element. The length of the second actuating element is varied until the end of the second actuating element rests at the stop ring of the first actuating element, the transmission lever being in the position associated with the valve's open position. Then, both the blocking of the spring device is cancelled and the stop ring is removed from the first actuating element. The second actuating element displaces itself against the force of the auxiliary spring lying on the inside, as the control force of the spring device diminishes, until a balance has been achieved between the two forces of the springs. If there is a change of the position of the unsprung vehicle part relative to the housing of the braking pressure control unit a new balance will result between the springs. Thus two spring elements participate in the generation of the control force transmitted by the transmission lever to the valve device of the braking pressure control unit. This may result in a reduced accuracy of actuation.
It is thus an object of this invention to provide a braking pressure control unit of the type referred to where the auxiliary spring arranged between the actuating elements does not exert any influence on the control force.